Perhaps one the easiest things to do, is to cover it with an acoustically transparent ’fabric’ such as those available from 3rd-parties, like soundskin..

Here is one link (just as an example, others are available by searching online):

https://soundskins.com/product/soundskin-sub-charcoal/

The same way we used to fix car bodies? Resin-based filler, sanding, then a spray can?

A quick fix whilst you think about other solutions, a small piece of white electrical tape to cover the chip. Or possibly move the sub to different location, where the chip wont be so obvious.

Another quickie helper is to rotate the speaker 180°.

Hot glue gun, fine sandpaper and touch-up paint?

Or a home-made cover using acoustically transparent speaker cloth. A lot cheaper than a pre-made skin.

I have home-made covers on both my Subs, not to make them pretty but to keep critters from getting inside.

Cloth: https://smile.amazon.com/gp/product/B01HMBKNSS/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1